Number of Outlet Streams

The correct assignment of outlet streams ensures the consistency of the material balance. Remember that all the species - products, byproducts and impurities -should leave the process in outlet streams Some guidelines are given below  

Examine carefully the composition of the outlet reaction mixture. 

Order the components by their normal boiling point. 

Group neighboring components with the same destination. 

The number of all groups minus the recycle streams gives the number of the outlet streams. Azeotropes or solid components may change the rule. 

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Next, the mnimum number of simple separation units must be determined. Although there are single units that produce multiple output streams (such as a petroleum refining pipe still with many side draws), most units accept a single inlet stream and produce two oudet streams. For such simple separators, we need at least (iV-1) units, where N is the number of outlet streams (products, by-products, and waste). There are two types of questions to answer concerning these units in the separation section (1) What types of units should be used and (2) How should the units be sequenced ... 

The above expression indicates that the number of overall mass transfer units, Nqg, is only controlled by the concentrations of the solute in the inlet and outlet gas streams. 

Given a number Nr of waste (rich) streams and a number Ns of lean streams (physical and reactive MSAs), it is desired to synthesize a cost-effective network of physical and/or reactive mass exchangers which can preferentially transfer a certain undesirable species. A, from the waste streams to the MSAs whereby it may be reacted into other species. Given also are the flowrate of each waste stream, G/, its supply (inlet) composition, yf, and target (outlet) composition, yj, where i = 1,2,..., Nr. In addition, the supply and target compositions, Xj and x j, are given for each MSA, where j = 1,2, Ns. TTie flowrate of any lean stream, Ly, is unknown but is bounded by a given maximum available flowrate of that stream, i.e.. 

We turn now to the issue of material balance closure. Material balances can be perfect when one of the flow rates and one of the components is unmeasured. The keen experimenter for Examples 7.1 and 7.2 measured the outlet concentration of both reactive components and consequently obtained a less-than-perfect balance. Should the measured concentrations be adjusted to achieve closure and, if so, how should the adjustment be done The general rule is that a material balance should be closed if it is reasonably possible to do so. It is necessary to know the number of inlet and outlet flow streams and the various components in these streams. The present example has one inlet stream, one outlet stream, and three components. The components are A, B, and I, where I represents all inerts. 

Environment A number of melt water quality analyses of heavy metals, hydrocarbons, oxygen demands, and nutrients were made. From September 2001 to September 2002 measurements were made in the snow storage, in the stream where melt water is discharged and in the recipient, totally at seven locations. Reference measurements were made at a nearby location not affected by the outlet water. The results were compared with Swedish environmental quality criteria (SEPA, 1990 SEPA, 1999). 

This simple example illustrates the basic principles of water network design for maximum reuse for a single contaminant. A number of issues need to be considered that would apply to more complex examples. Consider Figure 26.25 involving three water mains and three operations. Operation 2 above the pinch terminates at a concentration less than the concentration for the high concentration water main. The outlet of Operation 2 must not be fed directly into this final water main. The basis of the mass balance from Figure 26.17 dictates that all streams must achieve the concentration of the water mains into... 

One would notice that there are a number of nonlinearities in the above constraints, more specifically in the contaminant mass balances around a unit and the central storage vessel. The nonlinearities arise due to the fact that the outlet concentration of each contaminant may not necessarily be at its respective maximum. Unlike the single contaminant case where one could replace the outlet concentration with the maximum outlet concentration, in the multiple contaminant case the outlet concentration of each contaminant remains a variable. Furthermore, the concentration within the central storage vessel is always variable, since the contaminant mass and mass of water within the vessel changes each time a stream enters or exits the vessel. To deal with this situation the following procedure is considered. 

Thirdly, the inlet and outlet concentrations were specified such that one was fixed directly and the other determined by mass balance using flowrate and mass load. However, a number of variations are possible in the way that the process constraints on quantity (or flowrate) present themselves. For instance, it could happen that there is no direct specification of the water quantity (or flow) in a particular stream, as long as the contaminant load and the outlet concentration are observed. Furthermore, the vessel probably has minimum and maximum levels for effective operation. In that case the water quantity falls away as an equality constraints, to become an inequality constraints, thereby changing the nature of the optimization problem. 

Gm is the molar flowrate of gas, W is the mass of solids in the bed, F is the number of moles of vapour adsorbed on unit mass of solid, and y0, y is the mole fraction of vapour in the inlet and outlet stream respectively. 

Ad, with the view of bringing the vapors over as much space as possible, that in the course of which they might deposit the quicksilver. Each of those chamber s has an outlet, s, by which the condensed metal flows out into a receiver, m m, whence it is conducted by a conduit, , into the main tenk. They have likewise an aperture at the top, which la closed, as also that at the base, during the period that the furnace is working. The last chamber in the scries is usually furnished with a number of flanges, or inclined boards, which reach in a slanting direction almost to the oppo-eito wall, upon which a stream of water is continually... 

For each stage, each stream is split into a number of streams equal to the number of potential matches which are directed to the exchangers representing each potential match. The outlets of each exchanger feature the same temperature and are mixed at a mixing point where the temperature of the considered stream at the next stage is defined. 

In most chemical processes reactors are sequenced by systems that separate the desired products out of their outlet reactor streams and recycle the unconverted reactants back to the reactor system. Despite the fact that process synthesis has been developed into a very active research area, very few systematic procedures have been proposed for the synthesis of reactor/separator/recycle systems. The proposed evolutionary approaches are always based upon a large number of heuristic rules to eliminate the wide variety of choices. Many of these heuristics are actually extensions of results obtained by separately studying the synthesis problem of reactor networks or separator systems, and therefore the potential trade-offs resulting from the coupling of the reactors with the separators have not been investigated. 

Pibouleau et al. (1988) provided a more flexible representation for the synthesis problem by replacing the single reactor unit by a cascade of CSTRs. They also introduced parameters for defining the recovery rates of intermediate components into the distillate, the split fractions of top and bottom components that are recycled toward the reactor sequence, as well as parameters for the split fractions of the reactor outlet streams. A benzene chlorination process was studied as an example problem for this synthesis approach. In this example, the number of CSTRs in the cascade was treated as a parameter that ranged from one up to a maximum of four reactors. By repeatedly solving the synthesis problem, an optimum number of CSTRs was determined. 

As Figure 3 shows, strict application of Equation 1 results in 11 equations in 11 unknowns and an iterative solution for the design sequence. To circumvent this cumbersome calculation, the system permselectivity was used to estimate the number of stages required in the design sequence for the separation, and Equation (1) was then used to estimate the area requirements knowing the stage outlet compositions of the permeate and residual streams. 

Based mainly on the analytical results for single particle motion in impinging streams, Tamir derived a number of expressions for the two parameters for various flow regimes in the two cases with and without chemical reaction, in which the parameters such as the droplet size, the motion times of a particle in the accelerating and decelerating stages, particle to gas velocity ratio at the outlet of the accelerating tube, etc. were involved (see Eqs. 11.2 to 11.25 in Ref. [5]). 

To install streams for feeds, product, and intermediate connections, click the arrow to the right of the Material Streams box on the bottom left of the window and select Material. Moving the cursor to the flowsheet produces a number of arrows on the inlets and outlets of the various blocks. A feedstream is installed by first clicking the flowsheet and then clicking the arrow pointing to a feed valve. Figure 2.32 shows stream 1 connected to valve VI. Figure 2.33 shows the final flowsheet with all lines installed and some streams renamed for clarity. Save the file in an appropriate directory. 

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